1. Field of the Invention
The present invention relates to epoxy molding compositions. More particularly, the present invention relates to epoxy molding compositions which are particularly useful as encapsulants for light sensing devices.
2. Brief Description of Related Technology
Epoxy resin compositions are widely used for electronic packaging materials in the electronics industry and, in particular, as encapsulants for semiconductor elements and electronic circuits. Accordingly, epoxy resin-based compositions have been widely used in the formation of molding compositions for use as electronic packaging materials. Transparent epoxy molding compositions are well known for use as encapsulants in connection with light-emitting diodes (LEDs) for use in lighting applications in the electronics industry.
As a particular example, silicon-based devices are typically sensitive to light with wavelengths up to about 1200 nm. If the infrared (IR) light is permitted to enter the sensor, the sensor responds to the infrared light and generates a spurious signal.
Optical sensors that transmit visible light are commonly used in electronic applications, but can be susceptible to transmission of infrared light. Accordingly, visible light or optical sensors can use an infrared blocking element to prevent infrared radiation from entering the light sensor. Liquid crystal color filters may be used. These filters are electronically switchable because they include an electronically controllable liquid crystal element. By electronically controlling the polarization of the liquid crystal element, the light that is transmitted through the filter may be controlled. In this manner, a given wavelength band may be transmitted through a given filter. In effect, the liquid crystal color filter may be tuned to a particular color. The liquid crystal color filters may be tuned to a pair of colors and, through color combination, may produce a third color. Thus, a liquid crystal color filter may form a switchable shutter which can controllably produce red, green and blue primary color bands or complementary color bands such as cyan, magenta and yellow.
U.S. Pat. No. 6,208,393 to Bawolek et al. discloses a liquid crystal color filter that includes an infrared blocking dye integrated within the filter to prevent infrared radiation from adversely affecting the performance of the filter when used in an imaging system. The dye may be incorporated into a liquid crystal element in the filter or may be coated on components of the filter. Suitable dyes are transmissive of light in the visible range and substantially absorbent of light in the infrared range from approximately 800 nm to 1200 nm in wavelength.
EP 1 152 035 discloses a preform for a polyester resin composition blow molded product that includes a polyester resin and an infrared absorbing colorant, which is at least one colorant selected from a phthalocyanine infrared absorbing colorant and a naphthalocyanine infrared absorbing colorant, which has an infrared maximum absorption peak in the region of 700 nm to 2000 nm.
In some cases, dyes are included in polycarbonate filtering lenses, which are attached to visible light or optical sensors using clear epoxy compositions, to act as an infrared blocking element to prevent infrared radiation from entering the light sensor. Such two-part lens-epoxy systems are undesirable as they require additional steps during manufacture and are generally more expensive than using epoxy compositions alone.
Additionally, the heretofore known filters can be an expensive, in some applications an overly bulky, and in other cases provide an insufficient, solution to the problem of filtering infrared radiation.
Therefore, it would be desirable to provide encapsulant materials that are capable of transmitting visible light while blocking infrared light to act as filters for optoelectronic devices such as visible light or optical sensors.